Though not all issues addressed, some definite improvements in Steam version
First of all, the price is only $3.99, cheaper than the XBOX360 release.
Secondly, the game runs on Windows XP and more smoothly. My computer has an inferior graphics card (NVidia GeForce 6150LE), and otherwise my system is middle of the road to entry-level, I have seen no significant drop in frame rates at all during even the most hectic parts of the game. Everything remains smooth as silk.
Unfortunately, some flaws remain. There still aren't unlockable achievements (which is one of the major features of Steam games!!), no retro mode, and no world leaderboard. Also, the game simply is best suited for dual joysticks. There's no way to get around it, and that is without a doubt a part of the games retro appeal, recalling the thumb-blistering analogue sticks of arcade games (or so I've read about them-- not that I played a lot of arcade games; a bit before my time :-) ) Point being that it is hectic enough with dual sticks analogue, and with alternative control schemes it becomes hard to the point of losing fun. Still, it is fairly playable using a mouse to aim and the keyboard to move.
I don't have a gamepad to see if the compatibility issues have been worked out.
If you like simple shooters with a lot of flash, I would recommend to at least give it a shot. It's good for a quick spin every so often, and at worse you're only out $3.99.